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The medication they inject is placed accurately, at the level of the facet joint, to target the "medial branch" of the nerve -- and theoretically the nerve at the joint itself.
They do this by using fluoroscopic guidance (essentially xrays) in the procedure room to ensure the needle is where it is supposed to be before injecting the medication.
The neck muscles ideally will feel better after the procedure, as the nerve irritation is improved as well.
Injections directly into the muscles themselves are generally called "trigger point" injections, and do not require xray guidance.
As both the deep dorsal spinal muscles and the facet joints are innervated by the medial branch of the dorsal rami, and the facet joints are innervated by more than one level of spinal nerve, how can you be sure that pain is coming from the joint? Derek
You can't be certain in any case, because, as you mention, there is multiple innervation of the joints as well as the muscles.
However, in most cases, it is felt that the nerve irritations in degenerative spinal conditions is coming from the pathologic joint (which may have degenerative arthritis, or instability), and thus putting the medication in this area is thought to be fairly diagnostic.
There is no MRI or CT or injection that can definitively tell with 100% certainty where pain is coming from, and that is something I stress to every patient. However, blocking the nerves at the facet joint can help to determine if that is a likely source of the pain.
Thank you for your answer. The reason for my question is that facet joint injection is considered the 'gold standard' for diagnosis of cervicogenic headache (you may not agree with this nomenclature). Literature focuses heavily on the degenerative joint being the primary source of nociception in this case. However manual techniques such as manipulation, massage, trigger point therapy all have evidence that they reduce or eliminate headache when applied in the suboccipital area. None of these therapies is likely to have changes on the degenerative articular surfaces or periarticular tissues. Perhaps then the facet joint injection is blocking all input from the medial branches and reducing the input into centrally sensitised system?
Yes, those techniques are designed to help with symptomatic relief --e.g. the muscles -- causing the pain.
However, if they feel that nerve irritation at the facet is causing the mucles to spasm, then it would make sense that you should feel some pain relief with an injection in that area, and people often do have a significant amount of relief (usually temporary) with a facet injection. But that is helpful information for your doctors regardless. The goal of the injection, as you mention, is to try and block the input and thus, make you feel better due to the pain being "blocked".